Researchers study tin whiskers in electronics

Tin whiskers on variable air-spaced capacitor in a radio tuner assembly (vintage 1960s)

Correction appended.

On May 19, 1998, the Galaxy IV satellite suffered an on-orbit failure that resulted in a massive telecommunications disruption on Earth. Around 45 million pagers went out of service that day, among other communication outages. The failure of the satellite control processor was attributed to an extraordinarily thin, crystalline, hair-like growth on the electromagnetic switch, known as tin whiskers.

Tin whiskers — which average 2–4 microns in diameter, or 1/100 of the diameter of a human hair — grow from the tin coating on copper wires and are common in electronics such as iPhones, digital cameras, watches and laptops. When the whiskers come into contact with a circuit, they can cause it to short.

Tin whiskers were first identified in the 1940s by Bell Laboratories. Like many companies, Bell used copper because of its high conductivity, but copper oxidizes quickly, impeding the performance of electronics. To prevent such oxidation, scientists recommended placing a protective coat of tin over the copper. Though this served as a temporary solution, the company found that their electronics would fail due to thin, metal fibers that formed from the tin.

Brown’s foray into tin whisker research began with the senior project of LucineReinbold ’01 MS’03PhD’07, which expanded into one of the primary research activities in the laboratory of Eric Chason, professor of engineering.

NitinJadhav, a postdoctoral researcher and student of Chason, said the whiskering process begins with a reaction between tin and copper. The copper goes into the tin, increasing the volume of the tin layer, which attempts to expand but cannot.

Jadhav used the analogy of a sealed, full tube of toothpaste. “If you have a tube of toothpaste, and you punch a hole, all the toothpaste is going to come out as a wire.” Likewise, he said, the stress inside the tin layer builds until it cannot contain the pressure any longer, eventually sprouting hairs.

In 2009, Brown researchers designed an automated electron microscope to better observe the process. They won the 2011 William N. Findley Award in “Mechanical Behavior of Materials” for a study in which they used this microscope.

Jadhav likened the automated system to Google Maps, explaining that it first takes a large snapshot of an area, then a high-resolution image of a smaller area, and then even smaller areas every ten minutes. This automated process, conducted over a period of 10–15 days, enabled researchers to see whiskers not only bud, but grow, since the same area could be revisited as often as needed without losing information about the other areas.

If people see whiskers inside an electronic device, they may assume the whiskers are not harmful if the device is still functioning properly. Even though the whiskers may be physically touching a circuit, the whiskers may not carry any electric current due to a tin oxide coating.

But recent NASA research has shown that these whiskers can still be harmful, since mechanical wear of the device — such as the jiggling of a car ­— can cause the coating to break down and the circuit to short, said Henning Leidecker, chief parts engineer at the Goddard Space Flight Center.

NASA became interested in tin whiskers after talking to the Boeing Aircraft Corporation in 1998. “We said, ‘My goodness, we should learn more about that,'” Leidecker said.

To reduce the growth of tin whiskers, electronics manufactures for decades had mixed small amounts of lead into their tin coating, Leidecker said. But in recent years, heightened awareness of lead poisoning has led to criticism of this practice.

The European Union responded to the criticism in 2006 by banning the use of lead and requiring companies to switch to a solder that consisted almost entirely of tin, with a tiny amount of copper.

The Swatch Company found that as a result of the switch, 30 percent of its watches developed whiskers, and many of those watches failed due to short circuiting. Swatch’s lawyers petitioned the EU to put lead back in the solder, touting evidence that the yearly quantity of lead used by Swatch only amounted to the quantity of lead in two car batteries, Leidecker said.

Lead has not been banned by all 50 states, Jadhav said.

“The Swatch Company itself didn’t actually say that it had a problem with tin whiskers. That’s a typical event,” Leidecker said. He noted that often, NASA does not hear about tin whisker problems until they cause a medical or security emergency, such as when the Food and Drug Administration called for the return and replacement of pacemakers due to tin whisker growth.

He recalled that the day that the Galaxy IV failed, a doctor told him it was the only day in years that she didn’t receive any pages.

“With 45 million pagers being disabled for a day, do you think anybody might have died because people weren’t available? Nobody pays attention to that. That’s not part of public record keeping, as far as I know,” Leidecker said.

Gold has been suggested as an alternative to lead, but given that it is about 500 times more expensive, it is not a cost-effective alternative, Leidecker said.

He added that conformal coating, a coating used to protect electronic circuitry from moisture and contaminants, can reduce the formation of tin whiskers.

But as of now, Leidecker said, there are not any good methods that will completely prevent the growth of tin whiskers.

Due to an editing error, a previous version of this article incorrectly attributed a quote about the Swatch Company and an anecdote about the Galaxy IV failure to NitinJadhav. In fact, Henning Leidecker was the source for those paragraphs. The Herald regrets the error.trong>